Portable electronic devices such as laptop computers, cellular phones, portable electronics, small light-weight electrical equipment or future electric automobiles are becoming commonplace and very popular. An important aspect of their performance, however, is battery life and cycle life and this has driven a number of technological developments in secondary lithium-ion batteries, which are commonly be used in such device. A high energy density material is a crucial aspect to satisfy marketable demand for high-performance lithium-ion batteries which demand seeks a battery with several hours of use between charging cycles, and also with a long cycle life, that is to say the performance of the battery remains generally constant over multiple charging cycles.
As one of negative electrode materials of secondary lithium-ion batteries, lithium metal is a very attractive material due to its ultrahigh specific capacity, 3860 mAh/g. However unavoidable lithium dendrite caused by the lithium precipitates can bring out serious safety problems. After many investigations, in 1991, a lithium “rocking chair” battery was successfully commercialized with carbon as an electrode negative material. In addition to safety, the advantages of carbon are that it is inexpensive, non-toxic, with a relatively high specific capacity.
Currently, graphite is widely used for the negative electrode materials for commercially available secondary lithium-ion batteries. For graphite, typically the theoretical limit capacity is 372 mAh/g corresponding to LiC6, depending however on its microstructure. See, for example, J. R. Dahn et al, Mechanisms for Lithium Insertion in Carbonaceous Materials, Science, Vol. 270, 590-593 1995. Such a specific capacity cannot, however, meet with the increasing requirements of much higher energy-density power supplies for modern-day electronics and possibly electric vehicles.
After the discovery of carbon nanotubes, people paid close attention to their electrochemical performance. See, for example, Guangli Che et al, Carbon nanotube membranes for electrochemical energy storage and production, Nature, Vol. 393, 346-349, 1998. As a kind of active material, the introduction of carbon nanotubes into the negative electrode of a secondary lithium battery is disclosed in U.S. Pat. Nos. 6,280,697, 6,709,471, 20030099883 as well as technical papers such as: Zhou et al, Electrochemical intercalation of single-walled carbon nanotubes with lithium, Chem. Phys. Lett. Vol. 307, 153-157, 1999; Agnes et al, Solid-State Electrochemistry of the Li Single Wall Carbon Nanotube System, J. Electrochem. Soc., 147(8) 2845-2852 2000; E. Frackowaiak, et al Vol. 37 61-69, 1999 Electrochemical storage of lithium multiwalled carbon nanotubes; Leroux F. J Power Sources Vol. 81, 317-322 1999 Electrochemical insertion of lithium in catalytic multi-walled carbon nanotubes. However, although the carbon nanotubes showed a very high capacity for the first and second cycle when used as the negative electrode material for a secondary lithium-ion battery, the cycle-ability was very poor and thus to date there has been little in the way of practical applications for carbon nanotubes in commercial rechargeable lithium batteries.
An object of the present invention therefore is to provide a type of lithium-ion battery showing high capacity, high reversible efficiency, and much longer cycle life than commercially available graphite.